The present invention relates to detection of the angle of attack of an airfoil moving through the air and is particularly useful in piloting of aircraft, including light aircraft.
The flying of an aircraft is dependent on the generation of lift resulting from the movement of an airfoil through the air. The generation of lift results when the angle of the chord line of the airfoil relative to the apparent wind is within a relatively small range of angles, the acceptable range of angles of attack. As shown in FIG. 1, the angle of attack is defined as the angle between the airfoil chord line and the relative wind direction. The chord line is defined as the line that connects the trailing edge (A) of the wing with the center curvature (B) of the wing. This range of angles varies considerably from one airfoil design to another, but even so, is ordinarily not significantly higher than about 18 degrees for light aircraft. When the angle of attack exceeds its upper limit, air separates from the upper surface of the airfoil (wing) and results in a decrease in lift. This loss of lift, or stall, is generally associated with an inability of the wing to support the aircraft.
It is a well known safety feature of light aircraft to detect and inform the pilot of an excessive angle of attack because this is the primary indicator of conditions that accompany a stall, or loss of lift of the wings. Obviously, loss of lift at the wings is of major importance in the piloting of a plane. Providing a display on the instrument panel indicating the angle of attack provides the pilot with important information useful for maintaining a safe attitude while flying.
There have been prior attempts to provide an aircraft pilot with information from which the pilot can take corrective actions to avoid or minimize the entry of excessive angles of attack, but each prior effort has been subject to limitations in its utility for light aircraft. A major shortfall of known prior efforts has been their reliance on alternating current, a power source not generally available in light aircraft. These efforts have employed equipment that requires A.C. power for components such as synchro transmitters and servo repeaters. Also, potentiometers and gear trains have been employed to enhance signal resolution. These types of systems are costly to manufacture and thus, their use has been largely restricted to large expensive aircraft.
Prior systems based on A.C. power supplies generally have required a method of amplifying the small detected angle for proper viewing by the pilot on a rotary dial spanning 360 degrees. Most cockpit indicators require a servo repeater and a gear train to amplify the sensed indication for meaningful viewing by the pilot. One such system is described in U.S. Pat. No. 3,475,958 issued Mar. 16, 1967 to Sabadishin and Argentieri (the inventor herein) and incorporated herein by reference. Since most indicator system currently employ a gear train to amplify the angle of attack angle of 18 degrees to approximately 360 degrees for best viewing and indication to the pilot, stops are employed at the transducer to maintain the system in mechanical synchronization. The need for approximately 360 degrees is because of the use of a rotary dial type indicator.
The stops, the gear trains and the related shafts have been a constant source of problems such as problems associated with slippage. Furthermore, there are substantial maintenance requirements for system calibration. The angle of attack system described herein addresses the cost and technical problems of the prior known efforts. Additionally, a display is provided that is vertically oriented rather than circular, thus providing an easy means to observe indication of angle of attack.